• 11 parts
  • Checked October 2026

Parts of a Flush Valve

A commercial flush valve cut open: name the diaphragm, relief valve, bypass, plunger and control stop.

Parts of a Flush Valve

Name Date

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1 2 3 4 5 6 7 8 9 10 11
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Write the name of each numbered part.Answer key

  1. Handle
  2. Valve body
  3. Cover
  4. Diaphragm
  5. Control stop
  6. Tailpiece
  7. Vacuum breaker
  8. Upper chamber
  9. Relief valve
  10. Bypass
  11. Plunger

Own drawing from plain geometry. Licence: own work.

Each numbered ring is a button. Use the arrow keys to move between them and Enter to choose. Names are read out in Study, and once a part is answered.

Next step Next: the urinal it flushes

All 11 parts on the diagram

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The flush valve 11

  1. Handle A push in any direction starts the flush.
  2. Valve body The main casting holds all the working parts.
  3. Cover The cap on top. It comes off to reach the diaphragm.
  4. Diaphragm A rubber disc that holds the valve shut between flushes.
  5. Control stop A valve on the supply. It sets the flow or shuts it off.
  6. Tailpiece The tube that joins the control stop to the valve body.
  7. Vacuum breaker It keeps water from being siphoned back into the supply.
  8. Upper chamber Water pressure here presses the diaphragm down on its seat.
  9. Relief valve The plunger tilts it. Water then escapes from the upper chamber.
  10. Bypass A small hole in the diaphragm. It slowly refills the upper chamber.
  11. Plunger The handle pushes it in against the relief valve.

How this list was compiled: Every name checked on 2026-10-01 and kept only where two of these use it of a manual diaphragm flush valve. (1) A flush valve maker's maintenance manual, read as page text on archive.org, https://archive.org/details/manualzilla-id-6328450 : valve body, valve body cover, inside cover, diaphragm with its orifice, relief valve, handle assembly, tailpiece, control stop (angle stop), vacuum breaker flush connection. (2) A second maker's installation and parts manual, https://archive.org/details/manualzilla-id-6946177 : valve body, valve body cover, diaphragm, by-pass orifice, handle, actuator rod, tailpiece, control stop, vacuum breaker tube, spud coupling and flange. (3) Plumbing textbooks and trade manuals, passages read through archive.org's full-text search: Plumbing: installation and design (1980), https://archive.org/details/plumbinginstalla0000sull , figure of a diaphragm flush valve (diaphragm, handle, plunger, relief valve, disc, guide, valve outlet, by-pass); Modern Plumbing (1987), https://archive.org/details/modernplumbing0000blan_m4h6 (diaphragm, upper chamber, lower chamber, handle, plunger, bypass, valve seat); Plumbers and Pipe Fitters Library, https://archive.org/details/plumberspipefitt00mcco (the greater pressure on top of the diaphragm holds it closed; the plunger tilts the relief valve and lets water escape from the upper chamber); a US Navy Utilitiesman course, https://archive.org/details/utilitiesmaniii024856mbp (water is forced into the upper chamber through the bypass). (4) Wikipedia, the article on this valve and Vacuum breaker, text only, https://en.wikipedia.org/wiki/Flushometer and https://en.wikipedia.org/wiki/Vacuum_breaker : a diaphragm divides a pressure chamber from the main supply, and a narrow passage refills it and so meters the flush; a vacuum breaker prevents water from being siphoned backward. Licence: own work

The drawing: Own drawing from plain geometry; nothing traced. Not to scale. Licence: own work

How it works

A flush valve flushes a toilet or urinal that has no tank, using the pressure of the water supply. Some people call it by the trade name flushometer. The drawing cuts a manual diaphragm valve open.

Read the full guide

The parts on the outside

Water comes from the wall through the control stop and the tailpiece into the valve body. A cover caps the body, the handle sticks out at the side, and the outlet runs down through the vacuum breaker to the fixture.

How a flush starts and stops

Between flushes, water in the upper chamber presses the diaphragm shut. Pushing the handle drives the plunger against the relief valve and tilts it. The upper chamber empties, the diaphragm lifts and water rushes to the fixture. The bypass then refills the upper chamber, and the diaphragm closes again.

  • The quiz takes auxiliary valve for relief valve, angle stop for control stop and by-pass orifice for bypass.

Questions and answers

What does the diaphragm do in a flush valve?

It is a rubber disc across the inside of the valve body. Water pressure in the upper chamber holds it down on its seat, which keeps the valve shut until the handle is pushed.

What is the bypass in a flush valve?

A small hole through the diaphragm. After a flush it lets water back into the upper chamber slowly, and that sets how long the flush lasts before the diaphragm closes.

What does the relief valve do?

It sits in the middle of the diaphragm. When the plunger tilts it, water escapes from the upper chamber, the pressure there drops and the diaphragm lifts to start the flush.

What is the control stop for?

It is a valve on the supply beside the flush valve. It sets how much water reaches the valve and shuts the water off when the valve is opened up.

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